This invention relates to the manufacture of integrated circuits and more particularly to methods for bonding gold wire interconnections to copper metallization.
In the evolution of semiconductor manufacturing, one of the enduring technologies is wire bonding. Wire bonding was used to interconnect the earliest IC chips to lead frames to make single IC packages. As the chip technology developed, more complex packages with higher levels of chip integration, e.g. multichip modules, were required and the need arose for interconnecting these modules to each other and to support boards. TAB bonding and bump bonding evolved as efficient interconnect technologies for these packages, but wire bonding is still a cost competitive technology, and wire bonding applications remain in current IC manufacture.
In the development of IC interconnect technology, copper was identified early as a desirable candidate for IC interconnections. Copper is highly conductive, is inexpensive, and the metallurgy of copper was well developed. However, early experience with copper as an interconnect material was poor. Copper is electrolytically very active and causes migration problems in semiconductors. In wire bonded packages, copper metallization cannot be used since it readily alloys with gold wire bonds and Cuxe2x80x94Au alloys are not robust. Because of the known problems with copper, aluminum, an inferior conductor, became the material of choice for IC metallization. Acceptance of aluminum metallization became so entrenched that other options have remained in the background.
IC technology has now advanced to the point where the conductivity of aluminum is becoming a limiting factor in IC design. This has caused process designers to revisit metallization material options. One that has re-emerged as promising is copper. However, integrating copper metallurgy into current IC processing raises newer versions of the old problems. One of these is wire bonding gold wires to copper metallization.
We have developed a process for gold wire bonding to copper metallization. It involves forming a barrier layer on the copper, and forming an aluminum pad on the barrier layer. Gold wire is then thermocompression bonded to the aluminum pad.